Heater Control Valve

Replace the heater control valve that regulates coolant flow to the heater core, restoring proper heater function and temperature control.

Warnings

Tools required

Parts

• Heater control valve × 1 — Use OEM specification or equivalent for 390ci V8
• Heater hose clamps × 2 — 5/8 inch or as needed

Fluids

• Engine coolant (ethylene glycol) — 1 qt

Preparation

1. Ensure engine is completely cold to the touch
2. Place drain pan under radiator drain petcock
3. Locate heater control valve on firewall near heater hoses
4. Identify control cable or vacuum line attachment to valve

Procedure

1. 1

   Drain coolant from system
   Open the radiator drain petcock at the bottom of the radiator and drain approximately 1-2 gallons of coolant into the drain pan, enough to lower the coolant level below the heater control valve. You do not need to drain the entire system.
2. 2

   Disconnect control cable or vacuum line
   Locate the heater control cable or vacuum line connected to the heater control valve actuator arm. If cable-operated, use needle-nose pliers to remove the cable retaining clip and disconnect the cable end from the valve arm. If vacuum-operated, carefully pull the vacuum line off the valve nipple.
3. 3

   Loosen inlet hose clamp
   Using a flathead screwdriver or hose clamp pliers, loosen the hose clamp securing the heater hose to the inlet side of the heater control valve. Slide the clamp back along the hose away from the valve connection.
4. 4

   Loosen outlet hose clamp
   Loosen the hose clamp on the outlet side of the heater control valve and slide it back along the hose. Note the orientation of the valve for proper installation of the replacement.
5. 5

   Remove old heater control valve
   Twist and pull the heater hoses off both sides of the valve. Expect residual coolant to drain from the hoses and valve. Remove the old valve from the vehicle. Use shop rags to catch any coolant spillage.
6. 6

   Prepare hoses and new valve
   Inspect the heater hose ends for cracks, hardening, or deterioration. If damaged, trim back 1/2 inch or replace hoses. Clean the hose ends with a shop rag. Verify the new heater control valve matches the original in size, configuration, and control type.
7. 7

   Install new heater control valve
   Position the new heater control valve with the inlet side toward the engine and outlet toward the firewall/heater core. Push the heater hoses firmly onto both valve connections until they seat completely against the valve barbs.
8. 8

   Secure hose clamps
   Slide the hose clamps into position over the hose-to-valve connections. Position each clamp at least 1/4 inch from the hose end. Tighten the clamps securely with a screwdriver, ensuring the hoses cannot be pulled off by hand.
9. 9

   Reconnect control cable or vacuum line
   Reattach the heater control cable to the valve actuator arm and install the retaining clip, or reconnect the vacuum line to the valve nipple. Ensure the cable moves freely and the valve actuator responds to movement, or that the vacuum line is fully seated.
10. 10

    Refill cooling system
    Close the radiator drain petcock. Add fresh coolant to the radiator to bring the level back to the proper fill line. Start the engine and allow it to reach operating temperature with the heater on, adding coolant as needed to purge air from the system. Check for leaks around the new valve connections.

Reassembly

1. Install radiator cap securely after system is fully bled
2. Verify control cable or vacuum line operates the valve through full range of motion

Verification

• With engine at operating temperature, verify no coolant leaks at heater control valve connections
• Test heater operation by moving temperature control from cold to hot, confirming warm air increases
• Check coolant level after test drive and top off if necessary
• Verify heater control valve opens and closes properly by feeling temperature change in heater hoses when adjusting controls

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